The invention relates to a method of making an integrated circuit, including a composition of matter for electrodepositing of chromium, to uses of certain chromium salts for electrodepositing and to processes for electrodepositing chromium.
Chromium is a metal of high technical value based on its superior attributes. Coatings of chromium are highly resistant to corrosion and are showing great hardness, low abrasion, thermal resistance and a low coefficient of friction. Chromium is weather resistant and illustrates low tarnishing, is stable at temperatures up to 500° C. and is inert to most chemicals except hydrochloric acid and hot sulfuric acid.
Usually a chromium coating is used in two technical fields: a) decorative chromium-plating with layers up to 0.80 μm usually on a nickel surface, or b) functional chromium-plating with layers of more than 0.80 μm being usually electrodeposited directly on the surface for an increased hardness.
In addition, chromium may be electrodeposited as black chromium using high current density. These are layers rich in Cr2O3 used in the optical or electrical industry as well as for sun collectors.
Metallic chromium or compounds of chromium (III) are toxicologically harmless for humans whereas compounds of chromium (VI) are rated toxic and carcinogenic. The lethal dose of chromium (VI) after oral uptake is given in literature as 1 g/kg body weight (L. Roth, Giftmonographien—Chrom und Chromverbindungen, Ecomed, Landsberg, 1999). Chromic acid is damaging to the lungs and liver and has an etching effect on mucosas. During degradation of the chromium (VI) compounds in the body chromium (V) is formed as an intermediate, which is held responsible for the carcinogenic activity. Owing to that, electrodepositing from baths having Chromium (VI) is either forbidden in a large number of countries or may only be done under tight security measures.
Even though as described above the use of Chromium (VI) and its compounds is quite problematic it is still state of the art to electrodeposit chromium from baths having chromium (VI) compounds as reliable alternatives are still missing. All of these facts and disadvantages clearly indicate a strong need for improvement in the technical field of electrodepositing of chromium.
For these and other reasons, there is a need for the present invention.